This circuit delivers at its output a voltage that proportional to the amplitude of the input signal in a range of 36 dB. We found it in an American documentation from 1966.
This timer with 1 second accuracy was obtained in a 1973 documentation. The Buzzer is a low-power type...
The sensors in this circuit are NTCs and PTCs that work in a differential way by directly...
The presented circuit is suggested by Texas Instruments (www.ti.com) in its Application Report...